Apparatus for removing liquid metal from furnaces



May 27, 1958 F. sPAGNoLET-rl APPARATUS FOR REMOVING LIQUID METL FROM FURNACES Filed June 3, 1955 ATTORNEY United States PateritO,

APPARATUS FOR REMOVING LIQUID METAL FROM FURNACES Flix Spagnoletti, Echirolles, France, assigner to Pechiney,

Compagnie de Produits Chimiques et Electronietallurglques, Paris, France, a corporation of Francer A considerable number of furnaces in which metals are treated in a liquid state are emptied at the present time by being tilted. This is particularly the case with induction furnaces and the majority of furnaces used for light metals. This operation makes it necessary to construct the furnaces with a frame which is much more rigid and substantial than if they were fixed; also, the tilting system is very expensive. These drawbacks are the greater the larger the capacity of the furnaces; actually, the present tendency is to increase the individual capacity of the furnace and hence, it becomes essen tial to adopt a much more flexible and easier metal removing procedure. Y

The present invention, which is based on applicants investigations, makes it possible to avoid these drawbacks. According to one embodiment of the invention, the liquid metal is ejected from a movable conducting, semi-conducting or insulating crucible by the effect of centrifugal force produced by the rotation of the liquid by means of a polyphase rotating eld, obtained by energizing exciting coils supplied with electric current. The movable crucible, which is provided atits upper end with a lateral opening, is preliminarily placed in the furnace in such a way as to be continuously supplied with liquid metal until the furnace has been cornpletely emptied.

2,836, 3?' Patented May 27, 1958 ice* y tom of the furnace up to the discharge opening, the bottom being completely uncovered.

The two examples-embodiments-of the invention described below, which are given by way of illustrationv and not by way of limitation, will enable a better understanding of the invention. These two examples will be detailed with reference to the annexed drawings in which:

Figure l. represents in elevation an induction furnace provided with a device for the electromagnetic discharge of the liquid metal, according7 to one embodiment of the present invention.

Figure 2 represents a diagrammatic horizontal section of the same furnace with a schematic showing of the various windings for creating the rotating lield.

Figure 3 shows the several positions of the liquid metal surface before and during its discharge.

Figure 4 illustrates a vertical section of another ernbodiment of the present invention, being the embodiment brieiiy referred to earlier in the present specification.

Figure 5 is a simplified circuit diagram of the furnace windings and related switches.

inated magnetic sheets, provided on its interior with A rotating field induces'in a secondary a current, the

ment whereby, a centrifugal force is generated which forces the liquid against the wall of the crucible. This pressure forces the liquid to ascend along the wall until it reaches the lateral opening through which it escapes.

The angular speed of the liquid is a function of the speed of the rotating field, which can be predetermined by the number of poles of the inductor system and by its strength.

The high frictional resistance of the moving liquid produces very appreciable sliding. This sliding may be increased or diminished by respectively diminishing or increasing the energy transmitted to the secondary, that is, the strength of therotating field and, hence, the power absorbed by the apparatus.

This power can be regulated by modifying the voltage and/or the strength of the current supplied to the apparatus in various ways known to those skilled in the art, whereby it is possible to obtain a more or less rapid removal of the liquid metal and a more or less complete emptying of the furnace.

When suicient power is used, there remains at the conclusion of the discharge but a film of liquid metal having a thickness of the order of 2 to 3 mm.; this lm rotates, covering the walls of the furnace from the botslots 2 enclosing the conductors constituting the exciting (inducing) coils 3.

The ring 1 is positioned horizontally and is fastened inside an iron frame 4. Two covers 5 and 6 surround and protect the heads of the coils; the lateral portions 5 and 6 of the covers 5 and 6 are constituted of non-V magnetic metal in order to avoid magnetic losses. The lower cover 5 serves also as a support for the yapparatus. The upper cover 6 carries in its central portion an opening 62 through which is inserted the crucible 7, and which opening also serves for charging the furnace. A cover in the form of a plug 8 normally closes this opening.

The crucible 7 is positioned on a base 9 of refractory bricks and is surrounded with a highly refractory lining 10 having a thickness varying according to the operating temperature of the material being treated, which lining is either a conductor or an insulator depending on the composition of the crucible 7. The setting of the crucible 7 inside the magnetic core must be rigid in order to avoid its displacement either by the direct action of the rotating field on the crucible 7 if it be conducting, or by the liquid during the discharge. In the upper portion of the crucible 7, there is provided an opening 11 which extends into a trough 12 through which the liquid metal Hows olf outside the furnace.

The windings for this furnace (Figure 2) comprise a main coil or monophase winding 14 Vserving to rnelt (fuse) the product.V Its power is that required for operating the induction portion of the furnace.

One or two auxiliary windings 15, displaced or with reference to the main winding 14, according to whether it is desired to produce a two or three-phase rotating field, are also mounted on the ring 1. In the interest of simplicity, there have only been shown, in Figure 2, two slots per pole-phase.

The auxiliary windings 15 are designed for the power required for the ejection of the liquid and for an intermittent operation. If desired, the discharge may be carried out in less than 30 seconds. By a suitable switching scheme, diagrammatically illustrated in Fig. 5, either the principal coil alone is supplied with monophase current with insertion of a battery of condensers in parallel for the normal operation of the furnace, for

example, for fusion of metal, or else the three coils are supplied with three-phase current without using the condenser battery, for the discharge operation.

The` duration of the removal operation is very short and it is not necessary to compensate the three-phase power factor. In Figure 3, the line y16 indicates the level of the liquid at rest. As soon as current is sent -through for the removal operation, rotation commences and the surface of the liquid assumes the shape of a paraboloid 17 which lengthens out, as the peripheral speed increases. The liquid runs off through the opening 11 and, at the end of the removal operation, there remains but a liquid cylinder 18 of a very slight thickness.

The inductor winding 14 of this furnace, Figure 2, is placed laterally of the Crucible in lieu of being concentric thereto. As a result of this arrangement, the ux (e) which traverses theV Crucible is horizontal and the fictitious secondary coil is outlined (positioned) on the vertical cross section of the metal in the Crucible. An electrostriction effect, indicated by the arrows 19, produces mixing at the surface of the metal in the direction of the arrows 20, that is, from the edge of the Crucible towards the middle and perpendicular to the direction of the inducing flux. The cross collects in the middle of the crucible and on a restricted area, which facilitates its skimming (removal) from the bath.

This arrangement decreases magnetic leakage; thus, a furnace of this type has a higher cos qs than a furnace with a concentric winding of the same diameter, and/ or of the same capacity, Containing metal of the same nature.

Example II The embodiment of the apparatus diagrammatically shown in Figure 4 is directly based on the electromagnetic removal principle of the furnace previously described. The mechanicall arrangement of the apparatus has been modified so as to adapt it for its operation and to reduce, as much as possible, its transverse dimensions. A core 21, constituted of magnetic metal sheets, is provided on its circumference with slots 22 wherein are disposed solid or tubular conductors, and with water circulation depending onlits capacity. These conductors form a polyphase winding 23 which is supplied through the terminals 24. Polar extensions 25 at the lower part of the' corey extend the rotating field downwardly as much as possible.

A Crucible 26 of refractory material surrounds the core in order to protect/it mechanically and thermally from the liquid metal. .A cast iron cylinder 27, constricted at the bottom so as to leave an opening which is but a few centimeters in diameter, surrounds the crucible 26. An orifice 29 at the upperend of the cylinder 27 serves for the ejection of the metal.

A plate 30, rigidly suspended so as to prevent the apparatus from rotating as a result of the reaction ofthe couple created by the moving liquid, especially at starting, supports first the wound core by means of a shaft 31 and second, the Cast iron cylinder 27 by means of a cage 32 or a non-magnetic metallic ring. The joint (seal) 33 should be sufficiently tight so as to prevent the liquid from eventually passing to the upper end-of the apparatus.

In operation, the apparatus is submerged in the liquid metal up to a certain height C in such a manner that the upper level of the the metal, which has penetrated through the opening 28, is as close as possible to the polar extensions, or to the magnetic core in event the apparatus does not have polar extensions. The apparatus is then fixed in position and supplied with current. The liquid placed below the magnetic core starts to rotate and ascend, as shown by the dotted lines 34. The more the liquid enters the gap 35, the more the intensity of the rotating field increases, and the liquid is driven more and more rapidly up to the orifice 29, through which it flows out.

A vacuum is produced at D and the external liquid penetrates in its turn into the apparatus along a path indicated by the arrows 36. There is thus produced a suction effect through the opening 28, and an expulsion of liquid metal through orificeV 29. As the cylinder issubjected to the rotating field, it heats up and thereby facilitates the maintenance of the liquid to be discharged in a fused condition.

Selection `of cast iron for the external cylinder 27 is justified for the following reasons:

(l) This casing must be metallic in order to resist temperature and the centrifugal forces of the metal to be removed.

(2) It must be magnetic to facilitate the passage of the ux therethrough and hence, permit reduction of magnetizing current; at the same time, it should possess resistance in order to oppose a high impedance to the induced currents and hence, cause reduction of the torsion Couple.

This apparatus, which is somewhat similar in shape to the cast iron vase provided` with an opening at its lower end which is used for removing aluminum in electrolytic cells-commonly referred to as ower potcan replace the tilting system of large melting furnaces. It is sufficient to provide an opening in the furnace for the immersion of the lower portion of the apparatus in the 'liquid metal during the removal of the latter. The same apparatus can successively service several furnaces, thus making it possible to adopt stationary furnaces which are more economical from the vstandpoint of both Construction and maintenance.

The apparatus can also be used for the removal of metal from electrolytic cells.

'I' claim:

l. Apparatus for removing molten metal comprising in combination: a vessel constituting the Crucible of an electric furnace and in contact with the liquid metal to be removed; means for generating a lrotating vmagnetic field adjacent to but out of contact with the metal to be removed; a refractory casing disposed between the vessel and said generating means; and a discharge opening for the molten metal in the upper portion of said vessel.

2. An apparatus according to claim 1, wherein the said field generating means comprise a coil for supplying the heat required to produce-said liquid metal in the Crucible, andv means for selectively energizing said coil during the normal operation of the furnace.

3. Apparatus according to claim l, further characterized in that the said field generating means comprise a laminated core formed of horizontally disposed magnetic sheets and include an air gap, and windings disposed parallel to the walls of the Crucible, and said Crucible being disposed in said air, whereby the Crucible is traversed laterally by the rotary magnetic field generated by said windings.

References Cited in the tile of this patent UNITED STATES PATENTS 2,536,859 Tama Ian. 2, 1951 2,552,876 Tama ..e May 15, 1951 2,658,452 Donelian Nov. 10, 1953 2,669,931 Godbold Feb. 23, 1954 2,730,951 Donelian etv al. Jan. 17, 1956 UNITED STATES PATENT oEEICE CERTIFICATE OE CORRECTION Patent No., 2,836, 637 May 2'7, 1958 Fefllx Spagnoletti It is hereby certified that error appears in the printed specification of' the above numbered patent requiring Correction and that the said Letters Patent should read as corrected below.

Column 3; line 24,. for YThe crossn read e The dross e v n column .4, liney 58, claim 3, after Hairn and before the comme;I

insert m gap @ma Signed vand sealed this 12th day of August 195,8.,

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Ocer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE 0E CORRECTION Patent No., 2,836963'7 May 27, 1958 Flix spagnoletti It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 35 line 24, for "The crossn read The dross se; column w line 58;, claim 3, after "airn and before the .commay insert m gap =1= Signed and sealed this 12th day of August l958 (SEAL) Attest:

KARL H, MINE ROBERT C. WATSON Attesting Ocer Commissioner of Patents 

1. APPARATUS FOR REMOVING MOLTEN METAL COMPRISING IN COMBINATION: A VESSEL CONSTITUTING THE CRUCIBLE OF AN ELECTRIC FURNACE AND IN CONTACT WITH THE LIQUID METAL TO BE REMOVED; MEANS FOR GENERATING A ROTATING MAGNETIC FIELD ADJACENT TO BUT OUT OF CONTACT WITH THE METAL TO BE REMOVED; A REFRACTORY CASING DISPOSED BETWEEN THE VESSEL AND SAID GENERATING MEANS; AND A DISCHARGE OPENING FOR THE MOLTEN METAL IN THE UPPER PORTION OF SAID VESSEL. 